One of the known methods for printing an image, such as a character, a drawing, or a pattern, on a fabric, such as a woven fabric, a nonwoven fabric, or a knitted fabric, is pigment printing in which an aqueous pigment ink is used. Pigment printing is a method in which a printing agent that is a pigment composition including a color pigment and a binder resin is applied to a base material and, after a dry-curing step has been conducted as needed, the printing agent is fixed to the base material. Known examples of the above printing method include silk screen printing (e.g., see PTL 1) in which a pattern formed on a screen fabric is sequentially printed on a fabric; and ink jet recording (e.g., see PTL 2) in which an ink ejected from a nozzle is deposited on a fabric.
For preparing a printing agent, commonly, an aqueous dispersion containing a high concentration of a pigment (commonly referred to as “aqueous pigment dispersion” or “pigment dispersion”) is diluted with water, and a binder resin and other additives are added to the diluted pigment dispersion. In particular, since pigments are insoluble in water, a method for dispersing a pigment in an aqueous medium with stability has been studied in order to form an aqueous pigment ink by diluting the aqueous pigment dispersion with water.
One of the known methods for dispersing a pigment used for printing is a method in which a resin produced by neutralizing, with a basic substance, an alkyl-(meth)acrylic acid ester monomer, an aliphatic vinyl monomer including a carboxyl group, an aliphatic vinyl monomer including a non-carboxyl-group crosslinkable functional group, and an emulsion polymer having a molecular weight of 2,000 to 20,000 is used as a pigment dispersant (e.g., see PTL 3). In the above method, a crosslinking reaction is conducted at 100° C. or more using a water-soluble fixing agent including a crosslinkable functional group, and a heating step needs to be conducted.
Examples of an aqueous pigment dispersion which does not require a heating step include, in the field of ink jet recording, a method in which a synthetic resin having a specific acid value, a base, and a colorant are sufficiently mixed with one another with a stirring machine or a dispersing device in the presence of an organic solvent, such as a ketone solvent or an alcohol solvent, in order to dissolve or disperse the colorant and make the synthetic resin self-water dispersible, and the resulting colored resin solution is mixed with an aqueous medium such that the small droplets of the self-water dispersible resin solution including the colorant are dispersed in the aqueous medium (e.g., see PTL 4, Paragraph [0024]); a method in which a block polymer compound including a hydrophobic segment and a hydrophilic segment constituted by a hydrophobic unit and a hydrophilic unit is used as a pigment dispersant (e.g., see PTL 5); and a method in which an A-B block polymer ((An-Bm) block polymer) is used as a pigment dispersant, where A represents styrene, B represents acrylic acid, the degree of polymerization of A is about 5 to about 50, and the degree of polymerization of B is about 70 to about 800 (e.g., see PTL 6).
The above methods are suitably used for producing a water-based ink for ink jet recording, but may cause coarse particles to be formed in the ink. In screen printing, coarse particles included in a printing agent increase the likelihood of a screen clogging when the screen is a high-mesh screen. Furthermore, in ink jet recording, the coarse particles may cause ink-ejection failure and degrade the preservation stability of an ink. The printing properties achieved by using printing agents produced by the above methods are not described in the above patent documents.